Plants engineered to be stress tolerant are known in the art. Stress tolerance in plant cells and plants can, e.g., be achieved by reducing the activity or the level of the endogenous poly-ADP-ribose polymerases (PARP) or poly(ADP-ribose) glycohydrolases (PARG) as described in WO00/04173 and WO04/090140, respectively.
European patent application No. 04077624.7 describes that stress tolerance in plants and plant cells is achieved using nucleotide sequences encoding enzymes involved in the NAD salvage synthesis pathway and/or the NAD de novo synthesis pathway e.g. for overexpression in plants.
However, none of these documents disclose the possibility to use the stress tolerance genes mentioned therein for obtaining tolerance to hypoxic or anoxic conditions in plant cells and plants. Neither do they disclose the use of the stress tolerance genes described therein for the purpose of allowing the root system of the plant to penetrate deeper into the growth medium or the soil.
The application of compounds of the class of neonicotinoids on plants for purposes other than insect control is also known from the art (WO 01/26468, WO 03/096811).
WO 01/26468 discloses a method of improving the growth of plants comprising applying to the plants or the locus thereof at least one compound selected from the class of the neonicotinoids.
WO03/096811 describes that the yield and/or the vigor of an agronomic plant can be increased or improved in locations where the level of insect infestation below that indicating the need for the use of an insecticide for insect control purposes by treating a seed of the plant with a neonicotinoid compound. The method is deemed useful for non-transgenic plants and for plants having a foreign gene that encodes for the production of a modified Bacillus thuringiensis delta-endotoxin protein.
None of these documents however describe the use of compounds of the class of the neonicotinoids on plants for the purpose of increasing the tolerance of plant cells or plants to hypoxic or anoxic conditions or to allow the root system of the plant to penetrate deeper into the growth medium or the soil.
Thus, the art remains silent on methods to increase the depth of penetration of a root system or roots of a plant into the growth medium or soil, or to increase tolerance of plant cells or plants to hypoxic or anoxic stress conditions using stress tolerance genes or by application of a chemical compound of the neonicotinoid class to plants, or cells thereof as described hereinafter in the different embodiments and claims.